A conventional alarm circuit for the residual capacity of a battery in a portable radio transmitting and receiving apparatus, when the residual capacity of the battery loaded in the apparatus lowers and reaches a given voltage value or less during talking, sounds an alarm from a sound source to inform the user of the apparatus that the residual capacity of the battery will soon become zero, and, a predetermined given period of time after the initiation of sounding of the alarm, breaks the circuit of a power source of the apparatus.
In the conventional alarm circuit for the residual capacity of a battery in a portable radio transmitting and receiving apparatus, wherein the circuit of the power source of the apparatus is broken a predetermined period of time after the initiation of sounding of the alarm, however, there are disadvantages in that the time taken from the beginning of sounding of the alarm to the breaking of the circuit of the power source is so short that there is a possibility that necessary talking cannot be conducted. An additional problem of the conventional alarm circuit is that once the alarm begins to sound, the sounding of the alarm continues until the circuit of the power source is broken, making it difficult to catch what the person talks.